1. Field of the Invention
This invention relates generally to apparatus for reproducing a video signal as a slow-motion picture, and more particularly, is directed to video tape recording and reproducing apparatus (VTR) of the type in which successive fields of the video signal are recorded in parallel oblique tracks on a magnetic tape and a slow motion effect is achieved by intermittently advancing the tape while reproducing fields of the video signal recorded in the oblique tracks scanned during each advancement and by repeatedly reproducing a video signal field recorded in an oblique track during each interval when the tape is at rest.
2. Description of the Prior Art
A VTR has been proposed in which two rotary magnetic heads having different head gap angles or azimuths alternately record successive fields of a video signal, along with respective pilot signals, in successive oblique tracks on a magnetic tape while the latter is transported at a normal tape speed. The pilot signals recorded in a predetermined number of the successive tracks constituting a group thereof have respective different frequencies in an order that is repeated cyclically for each of the track groups.
In a normal reproducing operation of the VTR, the successive tracks are alternately scanned by first and second rotary magnetic heads having azimuth angles corresponding to those of the heads with which the respective tracks were recorded and a reference pilot signal is provided with a frequency which, at any time, corresponds to the frequency of the pilot signal recorded in the track then intended to be scanned by a rotary magnetic head. Further, in the normal reproducing mode, if the scanning path of a rotary magnetic head deviates from the track intended to be reproduced thereby, the reproduced pilot signal contains a mixture of components respectively having the frequency of the pilot signal recorded in the track intended to be scanned and the frequency of the pilot signal recorded in the adjacent track toward which the scanning path deviates. From the reference pilot signal and the reproduced pilot signal, a tracking error signal is obtained which has an amplitude and polarity corresponding to the amount and direction of the deviation of the scanning path from the track intended to be reproduced, and the transportation of the tape, for example, by a capstan motor, is controlled to maintain accurate tracking during normal reproduction.
In a slow-motion picture reproducing mode of the previously proposed VTR, the magnetic tape is transported intermittently so that, during each of the successive intervals when the tape is at rest, rotary magnetic heads having the same head gap angles or azimuths repeatedly scan one of the oblique tracks recorded with such head gap angle for reproducing a still picture from the field segment of the video signal repeatedly reproduced from the scanned oblique track. A video signal synthesized to represent a slow-motion picture is derived from such still pictures and the fields of the video signal reproduced from the oblique tracks during tape transporting intervals between successive still picture intervals. Such slow-motion picture can be obtained with suppressed noise by controlling the scanning path of the rotary magnetic heads on the magnetic tape so as to minimize, during each still-picture reproducing interval, deviation of the scanning path from the lateral center of the track being scanned at the middle portion of such track considered in the longitudinal direction of the latter. In the previously proposed VTR, such noise suppression is intended to be achieved by correcting the scanning path of the rotary magnetic head or heads in response to the tracking error signal, derived as described earlier, during a tape transport period which precedes each still-picture reproducing interval, that is, at a time when the magnetic tape is being driven by the capstan motor. In other words, the scanning path of the rotary magnetic head or heads is corrected during the period in which the capstan motor is driven in response to the tracking error signal arising during such tape transporting period so that, in the next still-motion reproducing interval, the scanning path of the rotary magnetic heads on the magnetic tape will laterally bisect the middle portion, considered in the longitudinal direction, along the oblique track from which a field segment of the video signal is to be reproduced repeatedly. However, such scanning path of the rotary magnetic heads on the magnetic tape after the transportation of the magnetic tape is apt to be adversely influenced by variations in the torque of the capstan motor. Therefore, there is the danger that the scanning path of the rotary magnetic heads on the magnetic tape will not precisely laterally bisect the middle portion of the oblique track from which a field segment of the video signal is reproduced repeatedly after the transportation of the tape.
It has also been proposed to control the scanning path of the rotary magnetic heads in the slow-motion picture reproducing mode by means of a microcomputer, for example, as disclosed in Japanese Patent Application published before examination under Publication No. 60/202563. In this published application, a tracking error signal corresponding to a middle portion of a field segment of the video signal is converted to digital data by an analog-to-digital converter and written in a microcomputer for each field segment of the video signal reproduced repeatedly from one oblique track prior to the transportation of the magnetic tape. The digital data written in the microcomputer are compared with a data map stored in the microcomputer and, as a result of such comparison, there are obtained predetermined timing data for starting the acceleration and deceleration of a capstan motor in the following period during which the magnetic tape is to be transported. Based on such predetermined timing data, the times for starting acceleration and deceleration of the capstan motor are controlled so that, at the completion of a period during which the tape is transported, the scanning path of the rotary magnetic heads used for repeatedly reproducing a field interval of the video signal from one track on the magnetic tape will laterally bisect such track at the middle portion of the latter considered in the longitudinal direction therealong.
However, in the case where the scanning path of the rotary magnetic heads is controlled by a microcomputer, for example, as disclosed in Japanese Patent Application published before examination under Publication No. 60/202563, an analog-to-digital converter and a microcomputer for storing the data map are required and this results in a disadvantageous complication of the circuit configuration.